System and method to support full-time protection services in a network

ABSTRACT

Systems and methods are provided to implement a full-time protection mechanism and a new class of service offerings based on mechanisms to achieve an ‘always protected’ type of transport service for a networking environment where there may be multiple failures or synchronized attacks. This suite of services may utilize intelligent control plane technology in the optical transport network to support an ‘always on’ protection capability.

BACKGROUND INFORMATION

Traditional transport services in a connection-oriented network offerlimited protection capabilities for services riding over the network.These protection schemes generally use a pre-planned protection path toback up the working path, thus only providing back up protection for thefirst failure. As a result, protection from subsequent failures isgenerally not supported. For example, to guarantee fast protectionswitching performance (e.g., <100 ms), three commonly used protectionschemes are ‘1+1 protection,’ ‘1:1 protection,’ and ‘1:N protection.’

A service with 1+1 protection provides a customer with a pair ofdedicated ‘working’ and ‘protect’ paths. With 1+1 protection, when theworking path fails, a switchover to the protect path will occur enablingthe customer to still receive its service. In the transport network, theprotect path is pre-allocated, reserved, dedicated bandwidth which isused to simultaneously carry the same traffic as the working path.

A service with 1:1 protection provides a customer with a ‘working’ pathand a shared ‘protect’ path. The scheme allows the protection path to beused to carry other preemptable traffic when the working path is in anormal operating mode. When the working path fails, the scheme willpreempt the existing traffic on the protection path, then switch trafficon the previous working path over to the protect path enabling thecustomer to still receive its service. With 1:1 protection, theprotection path is pre-allocated, but its bandwidth can be shared withother preemptable traffic.

A service with 1:N protection provides a single ‘protection’ path(either shared or dedicated) to protect N customers' ‘working’ paths.When any one of the N working paths fails, the scheme will switch in theprotection path to replace the failed working path. When all N workingpaths are in normal state, the protection path can carry otherpreemptable traffic, just as the 1:1 scheme does.

Three common limitations with current protection schemes and servicesare (1) When the protect path becomes the ‘active’ path (i.e., the new‘working’ path), effectively, there is no continuation of the sameprotection provided to the customer should the new ‘active’ path failand the original failed path has not been repaired, (2) When the protectpath fails while the working path operates normally, the protection forthe working path is lost, and (3) When both working and protect pathsfail, the communication is totally disrupted.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIGS. 1A-1D show a high-level process flow diagram for providingfull-time protection services in accordance with one embodiment of thepresent invention;

FIGS. 2A-2C show exemplary embodiments of a full-time protection servicein the context of a ‘1+1 protected path’ request;

FIGS. 3A-3C show exemplary embodiments of a full-time protection servicein the context of a ‘1:1 protected path’ request;

FIGS. 4A-4C show exemplary embodiments of a full-time protection servicein the context of a ‘1:N protected path’ request; and

FIG. 5 shows the types of message flows that can be used in an opticaltransport network (OTN) when carrying out embodiments implementedaccording to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments according to the present invention(s) now willbe described more fully hereinafter with reference to the accompanyingdrawings, in which some, but not all embodiments of the invention(s) areshown. Indeed, the invention(s) may be embodied in many different formsand should not be construed as limited to the embodiments set forthherein; rather, these embodiments are provided so that this disclosurewill satisfy applicable legal requirements. Like numbers refer to likeelements throughout.

Embodiments of the present invention can be used to provide a full-timeprotection mechanism and a new class of service offerings based onmechanisms to achieve an ‘always protected’ type of transport servicefor a networking environment where there may be multiple failures orsynchronized attacks. In one embodiment, this suite of services canutilize intelligent control plane technology in an optical transportnetwork to support an ‘always on’ protection capability. For example,when there is a failure of the working path and a switchover to the‘protect’ (or protection) path occurs, a request can be sent to thecontrol plane in the optical transport network to create a new protectpath in the network.

By automatically creating a new protect path in response to theoccurrence of a protection switching event, the system ensures that aprotect path will be available in case of yet another failure. Each newprotect path can be created as needed, thus enabling a customer tocontinue to have protection for their service regardless of how manyfailures may occur. Such embodiments may provide carriers with theability to offer, for example, new protection services and service levelagreements for transport-based services (e.g., private line, Ethernet,SAN, wavelength), for data services (e.g., Layer 2 Ethernet, IP-VPN),and for other higher layer service offerings (e.g., Services over IP,Voice over IP). Embodiments implemented according to the presentinvention are capable of enhancing the current ‘two-strike and out’protection mechanisms by providing an ‘always on’ protection capability.Furthermore, this capability does not require pre-reserved ‘dedicated’bandwidth. Instead, the bandwidth allocated to each new protect path maybe selected dynamically from a pool of available bandwidth resources inthe network.

As will be described in further detail below, architectures implementedin accordance with the present invention may include the use of anintelligent control plane in a connection-oriented network, and a‘protection policy server’ for use in carrying out some or all of thedecision making processes associated with coordinating the dynamicestablishment of protection (and working) paths in a timely manner. Inone embodiment, the network through which such paths are created may bethe optical transport network (OTN). As would be readily understood byone of ordinary skill in the art, network elements that comprise theoptical transport network include, but are not limited to,next-generation SONET (NG-SONET), multi-service provisioning platforms(MSPP), next-generation dense wave division multiplexing (NG-DWDM),reconfigurable add/drop multiplexers (ROADM), and wavelength switchingnetwork elements.

Nearly all next-generation optical-transport-network platforms supportan intelligent control plane. The control plane in, for example, theoptical transport network generally includes those functions related tonetworking control capabilities such as routing, signaling, and resourceand service discovery, to name just a few. An intelligent control planeused in connection with embodiments of the present invention wouldpreferably support some or all of the following capabilities:auto-discovery and self-inventory of network resources, topology, andconnection map; end-to-end path calculations subject to trafficengineering constraints; dynamic end-to-end path setup and teardown in asingle-step and single-ended fashion; and support for a variety ofprotection and restoration schemes. Upon request, the control plane canbe used to establish both working and protect paths through the network.The request to provision such paths may be based on a request fromeither a management system or a client device, for example. If therequest is issued from a management system, the management system may bean element management system (EMS), a network management system (NMS),an operations support system (OSS), or any other management system thatmay be known or in use at the time.

As indicated above, the ‘protection policy server,’ as the term is usedherein, can be a component in the network that carries out some or allof the decision-making processes associated with coordinating thedynamic establishment of protection and/or working paths in a timelymanner. In one embodiment, all protection paths can be established bythe OTN control plane using specific routing or path constraints basedon the current resources and characteristics of the network. Theprotection policy server (PPS) may be a standalone software module, or,in another embodiment, it may be integrated into either a networkmanagement system or an operations support system. In yet anotherembodiment, the PPS may be a collection of interactive componentsdistributed throughout the network. The purpose of the protection policyserver is to function as the controller that keeps track of the workingand the corresponding protect (or protection) paths, and to determinewhen to notify the control plane to set up new protect (or working)paths. In determining what types of new protect paths need to becreated, the protection policy server can maintain information on theprotection and restoration policies associated with each existingservice. This may include, but is not limited to, information such asexplicit routing constraints, link cost, pre-emption, and diversityrequirements. It may also include information pertaining to servicelevel guarantees such as latency requirements.

FIGS. 1A-1D show a high-level process flow diagram for providingfull-time protection services according to one embodiment of the presentinvention. The process described in this embodiment begins (at 101)when, in response to receiving a request for service through a network,a network management system (NMS) establishes a working path and acorresponding protection path through the network in accordance with arequested protection scheme. The requested protection scheme can bebased on, for example, one of the protection schemes described above,such as ‘1+1 protection,’ ‘1:1 protection,’ or ‘1:N protection,’ or itmay be based on any other protection scheme known in the art. In oneembodiment, the request for service may be a request to set up aprotected path call between a first location and a second location in anoptical transport network. As will be illustrated below, such requestsmay originate from either a management system or from a client device,for example. If the request is issued from a management system, themanagement system issuing the request may be an Element ManagementSystem (EMS), a Network Management System (NMS), an Operations SupportSystem (OSS), or any other known management system that may be known orin use at the time.

The requested service can be established by directing the control planeportion of the network to provision a working path and a protect paththrough the network in accordance with the requested protection scheme.After the working and protect paths are established, the system (at 102)receives notification of the network segments that have been createdalong the working and protect paths. According to one embodiment, suchnotification(s) can be received at a ‘protection policy server.’ Asindicated above, the ‘protection policy server’ (PPS) is a component inthe network that carries out some or all of the decision-makingprocesses associated with coordinating the dynamic establishment ofprotection paths in a timely manner. Stated differently, the purpose ofthe PPS is to function as the controller that keeps track of the workingand the corresponding protect paths, and that determines when to notifythe control plane to set up new protect paths. With knowledge of thecurrent working-protection arrangement for the requested service, thesystem proceeds to wait for any protection switching notificationsassociated with such arrangement.

As indicated at step 103, so long as no failures occur on the workingand protection paths, the working and protection paths will continue tooperate according to the initial working-protection arrangementestablished above. The term ‘failure,’ as used herein, is to beconstrued broadly to refer to any event, requirement, motivation, etc.,that causes a particular path to become unusable for its intendedpurpose. When a failure does occur on the working path, for example, andthe protect path becomes the new working path (in accordance with thebasic protection scheme associated with the initial working-protectionarrangement), the protection policy server can be notified of theprotection switching event by an element management system or directlyfrom a network element. In some cases, protection switching may occurusing traditional Automatic Protection Switching (APS) functionality inthe network element associated with the failure, and the protect pathwill become the new working path. As would be readily understood by oneof ordinary skill in the art, the handling of failed working paths inall scenarios is implementation specific. For example, failed workingpaths can be torn down and their resources de-allocated immediately, orthey can be kept in a degraded state, pending repairs.

While the term “protection switching” is typically used herein to referto the act of reassigning a protection path to be the new working pathfor a failed working path, the term “protection switching event” broadlyrefers to any event that is associated with the operation or failure ofone or both of the working and protection paths in a working-protectionarrangement; similarly, the term “protection switching notification”broadly refers to any notification that is associated with the operationor failure of one or both of the working and protection paths in aworking-protection arrangement.

If a protection switching notification is received (103) by the PPS/NMS,indicating a failure in one or both of the working and protection paths,the process proceeds to step 104. At this stage, the system determineswhether the received notification is a “Case 1” notification, meaningthat there was a failure on the working path, and protection switchingwas successfully performed. If the answer to the question at step 104 is“no,” the process proceeds to step 109. However, if the answer to thequestion at step 104 is “yes,” meaning protection switching in the priorworking-protection arrangement was performed successfully, the processadvances to step 105, where the system determines what type of newprotection path (e.g., characteristics, routing constraints, etc) needsto be created to support the new working path. The protection policyserver may base this determination on one or more requirements orcharacteristics. For example, the type of new protect path to be createdmay be based on such information as explicit routing constraints, linkcost, pre-emption, and diversity requirements, to name just a few. Itmay also include information pertaining to service level guarantees suchas latency requirements.

In accordance with the determination made in step 105, the system (at106) establishes the new protection path for the new working path and.Subsequently (at 107), the system receives notification (e.g., via anEMS or directly from a network element) regarding the establishment ofthe new protection path and the current working-protection arrangement.At step 108, all resources allocated to the failed working path arereleased. The process then returns to step 103, where the systemcontinues to wait for other protection switching notifications to bereceived.

If the answer to the question at step 104 is “no,” the process proceedsto step 109, where the system determines whether the receivednotification is a “Case 2” notification, meaning that only theprotection path failed, and no protection switching event is needed. Ifthe answer to the question at step 109 is “no,” the process proceeds tostep 114. However, if the answer to the question at step 109 is “yes,”meaning protection switching is not needed, but restoration of thefailed protection path is, the process advances to step 110, where thesystem determines what type of new protection path (e.g.,characteristics, routing constraints, etc) needs to be created toreplace the failed one. Based on this determination, the system (at 111)establishes the new protection path to replace the failed one and,subsequently (at 112), receives notification regarding the establishmentof the new protection path and the current working-protectionarrangement. At step 113, all resources allocated to the failedprotection path are released. The process then returns to step 103,where the system continues to wait for other protection switchingnotifications.

If the answer to the question at step 109 is “no,” the process proceedsto step 114, where the system next determines whether the receivednotification is a “Case 3” notification, meaning that protectionswitching failed, due to the fact that simultaneous failures occurred onboth the working and protection paths. If the answer to this question isalso “no,” the process can proceed to step 121, where the system may beconfigured to handle still other types of protection switchingnotifications. However, if the answer to the question at step 114 is“yes,” meaning that both the working and protection paths have failed,the process advances to step 115, where the system determines what typeof new working path needs to be created to replace the failed one. Basedon this determination, the system (at 116) establishes the new workingpath to replace the failed one. Similarly, at step 117, the systemdetermines what type of new protection path needs to be created, and, atstep 118, establishes such new protection path to replace the failedone. At step 119, the system receives notification regarding theestablishment of the new working and protection paths and the currentworking-protection arrangement. At step 120, all resources allocated tothe failed working and protection paths are released. The process thenreturns to step 103, where the system continues to wait for otherprotection switching notifications.

FIGS. 2A-2C show exemplary embodiments of a full-time protection servicein the context of a ‘1+1 protected path’ request. As described above, aservice with basic ‘1+1 protection’ provides a customer with a pair ofdedicated ‘working’ and ‘protect’ paths, where the protect path is usedto simultaneously carry the same traffic as the working path. When theworking path fails, a switchover to the protect path will occur enablingthe customer to still receive its service. As with other knownprotection schemes, basic ‘1+1 protection’ does not provide the customerwith a similar level of protection after a first failure occurs in theworking path (i.e., when the protect path becomes the active workingpath, there is no similar level of backup protection should anotherfailure occur). Accordingly, FIGS. 2A-2C depict a series of events thatillustrate how embodiments of the present invention can be used toprovide full-time protection to a customer requesting ‘1+1 protectedpath’ service through a network.

In particular, FIG. 2A shows an exemplary sequence of events that mayoccur when there is a failure in the working path of a ‘1+1’working-protection arrangement. In this embodiment, the process begins(at Step 1) with a request for a ‘1+1 protected path’ for a call betweena first client (Client A) and a second client (Client Z). This requestmay, for example, originate from either a network management system(NMS) or directly from a client device (e.g., Client A). The request forservice can be directed to an intelligent control plane that isresponsible for provisioning (Step 2) both the working and protect pathsthrough the network. As mentioned above, the control plane within aconnection-oriented network generally includes those functions that arerelated to networking control capabilities such as routing, signalingand resource and service discovery, to name just a few. In FIGS. 2A-2C(and subsequent figures), the control plane is graphically representedby the interconnection of network elements located below theelement-management-layer/network-element (EML-NE) interface.

A control plane consists of a set of routing and signaling protocolsthat enable a network to achieve automated functions. As indicatedabove, such functions may include auto-discovery and self-inventory ofnetwork resources, topology, and connection map; end-to-end pathcalculations subject to traffic engineering constraints; dynamicend-to-end path setup and teardown in a single-step and single-endedfashion; and support for a variety of protection and restorationschemes, to name just a few. In practice, the ‘control plane’ (or thefunctionality associated therewith) is implemented either distributivelywithin network elements throughout the network or centrally incentralized controllers that reside in separate platforms, which arealso known as control plane by proxy. Accordingly, both managementsystems (e.g., EMS1) and client devices (e.g., Client A) can communicatewith the ‘control plane’ portion of such network elements to requestthat certain operations be performed, such as the provisioning of a newworking or protect path as shown in Step 2.

If the request for service is made by a client device (e.g., Client A),the request can be directed to the control plane via a user networkinterface (UNI) connection, which connects the client to a particularnetwork domain (e.g., Vendor 1 Domain). If the request is instead madeby the NMS, the request may be passed to an appropriate elementmanagement system (e.g., EMS1), which then takes over responsibility fordirecting the control plane to provision both the working and protectpaths through the network. As would be readily understood by one ofordinary skill in the art, communication between a NMS and an EMS can befacilitated via an appropriate network management layer/elementmanagement layer (NML-EML) interface, using, for example, a “TMF513/608”(ver 3.5 and beyond) message set. Similarly, communication between a NMSand a network element within the control plane can occur via anappropriate network management layer/network-element (NML-NE) interface,using a vendor specific “TL1” message set. As would also be understoodby one of ordinary skill in the art, communications within the controlplane may include the following (and future versions of the following):(1) UNI messages specified in Off UNI 2.0 Implementation Agreement; (2)E-NNI signaling messages as specified in Off NNI 1.0 signalingImplementation Agreement; and (3) I-NNI signaling messages arevendor-specific, mostly based on IETF GMPLS signaling standards.

The working and protect paths (in this example) are shown passingthrough three different network domains (e.g., Vendor Domains 1, 2 and3), each of which is connected to the next via an externalnetwork-to-network interface (E-NNI) connection. After the control planehas been used to establish the initial working and protect paths, theprotection policy server (PPS) can be notified (either directly or viathe NMS) of all segments along both the working and protect paths. Asindicated in Step 3, such notification may occur via the one or moreelement management systems (e.g., EMS1) associated with the respectivenetwork domains located along the working and protect paths. Note thatin this embodiment, the PPS is depicted as being an integral portion ofthe NMS. However, in another embodiment, the PPS can be a standalonesoftware module configured to operate at a different point (or points)within the network.

Continuing with the present example, now suppose that (at Step 4) afiber cut on the working path triggers a protection switching event inwhich the (original) protection path is assigned to be the new workingpath. When this occurs, the PPS (at Step 5) can be notified via EMS1 orEMS3, for example, of the protection switching event and the new workingpath. In response to such notification, the PPS (at Step 6) can instructthe control plane (e.g., via EMS1) to provision a new path to be theprotect path for the new working path. As described above, the PPS canbe configured to determine the type of new protect path that needs to becreated based on, for example, the protection and restoration policiesassociated with this particular service. When the provisioning of thenew protect path is complete, the PPS (at Step 7) can be notified of thenew working path and protect path arrangement. By repeating theseactions each time a failure occurs in the current working path, thesystem can be configured to provide a customer with an ‘always on 1+1protection’ type of service.

FIG. 2B shows an exemplary sequence of events that that may occur, inaccordance with one embodiment of the present invention, when there is afailure on the protect path and not the working path of the ‘1+1’working-protection arrangement. In other words, suppose that (at Step 4)a fiber cut occurs on the protect path instead of the working path. Inthis case, no protection switching event would occur because the workingpath is still operational. However, the customer's working path is nowwithout the same level of protection it had prior to such failure on theprotect path. To remedy this, the PPS (at Step 5) can be notified viaEMS1 or EMS3, for example, of the protection path failure, and inresponse to such notification, the PPS (at Step 6) can instruct thecontrol plane (e.g., via EMS1) to provision a new protect path toreplace the failed protect path. When the provisioning of the newprotect path is complete, the PPS (at Step 7) can be notified (e.g., viaEMS1) of the new protect path, thus ensuring that the PPS is kept awareof the current working path and protect path arrangement.

FIG. 2C illustrates an exemplary sequence of events that may occur whenthere are simultaneous failures on both the working and the protectpaths of the ‘1+1’ working-protection arrangement. In this case, theprotection switching event that would be facilitated by the failure onthe working path would itself fail due to the simultaneous failure ofthe protect path. When addressing this situation, the PPS (at Step 5)can be notified (e.g., via EMS1 or EMS3) of the simultaneous failures onboth the working and the protect paths, and in response to suchnotification, the PPS (at Step 6) can instruct the control plane (e.g.,via EMS1) to provision a new pair of 1+1 working and protect paths toreplace the failed pair. When the provisioning of the new pair ofworking and protect paths is complete, the PPS (at Step 7) can benotified of the new 1+1 working and protect path arrangement.

FIGS. 3A-3C show exemplary embodiments of a full-time protection servicein the context of a ‘1:1 protected path’ request. As described above, aservice with 1:1 protection provides a customer with a ‘working’ pathand a shared ‘protect’ path. The scheme allows the protection path to beused to carry other preemptable traffic when the working path is in anormal operating mode. When the working path fails, the scheme willpreempt the existing traffic on the protection path, and then switchtraffic on the previous working path over to the protect path, enablingthe customer to still receive its service. As with other knownprotection schemes, basic ‘1:1 protection’ does not provide the customerwith a similar level of protection after a first failure occurs in theworking path. Accordingly, FIGS. 3A-3C depict a series of events thatillustrate how exemplary embodiments of the present invention can beused to provide full-time protection to a customer requesting ‘1:1protected path’ service through a network.

Specifically, FIG. 3A shows an exemplary sequence of events that mayoccur when there is a failure in the working path of a ‘1:1’working-protection arrangement. In this embodiment, the process begins(at Step 1) with a request for a ‘1:1 protected path’ for a call betweena first client (Client A) and a second client (Client Z). Once again,this request may originate from either a network management system (NMS)or directly from a client device (e.g., Client A), and the request canbe directed to an intelligent control plane that is responsible forprovisioning both the working and the shared protection paths throughthe network (as indicated in Step 2). If the request for service is madeby a client device, the request can be directed to the control plane viaa user network interface (UNI) connection, which connects the client toa particular network domain (e.g., Vendor 1 Domain). If the request ismade instead by the NMS, the request may be passed to an appropriateelement management system (i.e., usually the EMS that manages theoriginating NE—EMS1), which then takes over responsibility for directingthe control plane to provision both the working and the shared protectpaths through the network. Communication between the NMS and the one ormore EMSs may be facilitated via an appropriate network managementlayer/element management layer (NML-EML) interface.

In this example, the working path and the shared protect path are shownpassing through three different network domains, each of which isconnected to the next via an external network-to-network interface(E-NNI) connection. After the control plane has been used to establishthe initial working and protect paths, the protection policy server(PPS) can be notified (either directly or via the NMS) of all segmentsalong both the working and protect paths. As indicated in Step 3, suchnotification may occur via the one or more element management systemsassociated with the respective network domains located along the workingand protect paths.

Now suppose, for example, that (at Step 4) a fiber cut affecting theworking path triggers end points to perform 1:1 protection switching,which, in this case, includes preempting low priority traffic on theprotect path and assigning the (original) protect path to be the newworking path. When this occurs, the PPS can be notified (at Step 5) ofthe protection switching event and the change of the working path. Inresponse to such notification, the PPS (at Step 6) can instruct thecontrol plane to provision a new path through the network to be theprotection path for the new working path. Once provisioned, use of thenew protect path for other low priority traffic can also resume. Asdescribed above, the PPS can be configured to determine what type of newprotection path needs to be created based on, for example, theprotection and restoration policies associated with this particularservice. When the provisioning of the new protect path is completed, thePPS (at Step 7) can be notified (e.g., via EMS1) of the new protectionpath and the now current working-protection arrangement. By repeatingthese actions each time a failure occurs in the current working path,the system can be configured to provide a customer with an ‘always on1:1 protection’ type of service.

FIG. 3B shows an exemplary sequence of events that that may occur, inaccordance with one embodiment of the present invention, when there is afailure on the protect path and not the working path of the ‘1:1’working-protection arrangement. In other words, suppose that (at Step 4)a fiber cut occurs on the protect path instead of the working path. Inthis case, no protection switching event would occur because the workingpath is still operational. However, the customer's working path is nowwithout the same level of protection it had prior to such failure on theprotect path. To remedy this, the PPS (at Step 5) can be notified viaEMS1 or EMS3, for example, of the protection path failure, and inresponse to such notification, the PPS (at Step 6) can instruct thecontrol plane (e.g., via EMS1) to provision a new protect path toreplace the failed protect path. When the provisioning of the newprotect path is complete, the PPS (at Step 7) can be notified (e.g., viaEMS1) of the new protect path, thus ensuring the PPS is kept aware ofthe current working-protection arrangement.

FIG. 3C illustrates an exemplary sequence of events that may occur whenthere are simultaneous failures on both the working and the protectpaths of the ‘1:1’ working-protection arrangement. In this case, theprotection switching event that would be facilitated by the failure onthe working path would itself fail due to the simultaneous failure ofthe protect path. When addressing this situation, the PPS (at Step 5)can be notified (e.g., via EMS1 and/or EMS3) of theprotection-switching-event failure caused by the simultaneous failureson both the working and protect paths. In response to such notification,the PPS (at Step 6) can instruct the control plane (e.g., via EMS1) toprovision a new pair of 1:1 working and protect paths to replace thefailed pair. When the provisioning of the new pair of working andprotect paths is complete, the PPS (at Step 7) can be updated as to thenew 1:1 working and protect path arrangement.

FIGS. 4A-4C show exemplary embodiments of a full-time protection servicein the context of a ‘1:N protected path’ request. As described above, aservice with 1:N protection provides a single ‘protection’ path (eithershared or dedicated) to protect N customers' ‘working’ paths. When anyone of the N working paths fails, the scheme will switch in theprotection path to replace the failed working path. When all N workingpaths are in normal state, the protection path can carry otherpreemptable traffic, just as the 1:1 scheme does. As with other knownprotection schemes, basic ‘1:N protection’ does not provide the customerwith a similar level of protection after a first failure occurs in theworking path. Accordingly, FIGS. 4A-4C depict a series of events thatillustrate how exemplary embodiments of the present invention can beused to provide full-time protection to a customer requesting ‘1:Nprotected path’ service through a network.

Specifically, FIG. 4A shows an exemplary sequence of events that mayoccur when there is a failure on one of the N working paths of a ‘1:N’working-protection arrangement. In this embodiment, the process begins(at Step 1) with a request for a ‘1:N protected path’ for a call betweena first client (Client A) and a second client (Client Z). The request,which may originate from either a network management system (NMS), ordirectly from a client device, for example, can be directed to thecontrol plane portion of the network. Upon receiving the request for a1:N protected path, the control plane (at Step 2) can provision aworking path through the network and associate such working path with apre-provisioned shared protection path. The N working paths and theshared protection path, in this example, are shown passing through threedifferent network domains. The PPS can then be notified (e.g., via EMS1)of all segments along the working path and its association with theshared (pre-provisioned) protection path, as indicated in Step 3.

Now suppose that (at Step 4) a failure occurs on one of the N workingpaths (e.g., Working #1), which triggers end points to perform 1:Nprotection switching and assign the (original) shared protection path tobe the new working path for “Working #1.” When this occurs, the PPS canbe notified (at Step 5) of the protection switching event and the changeof the working path for Working #1. In response to such notification,the PPS (at Step 6) can instruct the control plane to provision a newpath to be the protection path for the new set of N working paths. Asdescribed above, the PPS can be configured to determine what type of newprotection path needs to be created based on, for example, theprotection and restoration policies associated with this particularservice. When the provisioning of the new protect path is complete, thePPS (at Step 7) can be notified of the new protect path and the currentworking-protection arrangement. By repeating these actions each time afailure occurs in the current working path, the system can be configuredto provide a customer with an ‘always on 1:N protection’ type ofservice.

FIG. 4B shows an exemplary sequence of events that that may occur, inaccordance with one embodiment of the present invention, when there is afailure on the shared protect path of the ‘1:N’ working-protectionarrangement. In other words, suppose that (at Step 4) a fiber cut occurson the shared protect path instead of one of the N working paths. Inthis case, no protection switching event would occur because the Nworking paths are still operational. However, the N working paths arenow without the same level of protection they had prior to the failureon the shared protection path. To remedy this, the PPS (at Step 5) canbe notified via EMS1 or EMS3, for example, of the failure on the sharedprotection path. In response to such notification, the PPS (at Step 6)can instruct the control plane to provision a new shared protect path toreplace the failed shared protect path. When the provisioning of the newprotect path is complete, the PPS (at Step 7) can be notified (e.g., viaEMS1) of the new protect path, thus ensuring the PPS is kept aware ofthe current working-protection arrangement.

FIG. 4C illustrates an exemplary sequence of events that may occur whenthere are simultaneous failures on at least one of the N working pathsand the shared protect path of the ‘1:N’ working-protection arrangement.In this case, the protection switching event that would be facilitatedby the failure on the (at least one) working path would itself fail dueto the simultaneous failure of the protect path. When addressing thissituation, the PPS (at Step 5) can be notified (e.g., via EMS1 or EMS3)of the 1:N protection switching failure caused by the simultaneousfailures on both the (at least one) working path and the shared protectpath. In response to such notification, the PPS (at Step 6) can instructthe control plane (e.g., via EMS1) to provision new working paths forall failed working paths, and create a new shared protect path toreplace the failed one. When the provisioning of the new working andprotect paths is complete, the PPS (at Step 7) can be updated as to thenew working paths and the shared protect path.

FIG. 5 illustrates the types of message flows that can be used in anoptical transport network (OTN) when carrying out embodimentsimplemented according to the present invention. For example,communications between a NMS that includes PPS service logic and an EMSmay occur using a “TMF513/608” message set or a vendor-specificextension of the message set. This exemplary message set, as would beknown to one of ordinary skill in the art, includes such commands as“establishCall,” “addConnection,” “getRoute,” “getConnection” and“releaseCall,” which allow the PPS/NMS to carry out the types offunctionality described above, including, but not limited to,establishing new working and protect paths, obtaining information onexisting paths and releasing previously allocated resources. The messageset also allows the EMS to provide the PPS/NMS with command responses(i.e., indicating the success or failure of previously submittedcommands) and alarm and status notifications (e.g., protection switchingnotifications, as discussed above). The right-hand portion of FIG. 5further illustrates how similar information exchanges can occur betweenthe PPS/NMS (or an EMS) and individual network elements in the OTN. Asmentioned above, communications to and from the network element leveltypically involve the use of vendor specific “TL1” message sets.

Although exemplary embodiments discussed above were described inconjunction with provisioning a new protect path after failure of aworking path, one or ordinary skill in the art would readily recognizethat it may also be desirable to reprovision a new protect path insituations where the working path stays up but the current protect pathexperiences a failure. In other words, the present invention explicitlycontemplates embodiments where a new protect path can be dynamicallyallocated in response to a failure in the previous protect path (insteadof the working path), thereby ensuring that the system (once again)maintains the same level of service by continuing to provide a backup(i.e., protect path) to the active working path.

In the preceding specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made thereuntowithout departing from the broader spirit and scope of the invention asset forth in the claims that follow. The specification and drawings areaccordingly to be regarded in an illustrative rather than restrictivesense.

1. A method, comprising: (1) establishing a current working pathcorresponding to a first path through a network between a first locationand a second location and a current protect path corresponding to asecond path through the network between the first location and thesecond location, the current working path and the current protect pathforming a current working-protection arrangement configured tofacilitate communication between the first and second locations; (2)receiving information associated with the establishment of the currentworking path and the current protect path; (3) receiving notification ofa failure of the current working path and the current protect path; (4)determining what type of new working path and new protect path need tobe created based at least in part on one or more protection policiesassociated with the working-protection arrangement between the firstlocation and the second location; (5) establishing the new working pathand the new protect path through the network between the first locationand the second location and releasing resources of the failed currentworking path and the failed current protect path; (6) receivinginformation associated with the establishment of the new working path asthe current working path and the new protect path as the current protectpath; and (7) repeating Steps (3), (4), (5) and (6) each time a failureoccurs on at least one of the current working path and current protectpath.
 2. The method of claim 1, wherein the notification received inStep (3) indicates that there was a failure on the current working pathwhich facilitated a reassignment of the current protect path to be thecurrent working path.
 3. The method of claim 1, wherein the currentprotect path is a dedicated protection path used to simultaneously carrythe same traffic as the current working path when the current workingpath is in a normal operating mode.
 4. The method of claim 1, whereinthe current protect path is a shared protection path that is used tocarry preemptable traffic when the current working path is in a normaloperating mode.
 5. The method of claim 1, wherein receiving informationassociated with the establishment of the current working path andcurrent protect path comprises receiving information identifying allsegments along both the working and protect paths.
 6. The method ofclaim 1, wherein said establishing steps are carried out via anintelligent control plane in an optical transport network.
 7. The methodof claim 1, wherein notification of the failure is received from atleast one of a network management system, an element management systemand a network element.
 8. The method of claim 1, wherein establishingthe new working path and the new protect path through the networkcomprises dynamically allocating bandwidth for the new working path andthe new protect path from a pool of available bandwidth resources in thenetwork, rather than from pre-reserved dedicated bandwidth.
 9. Themethod of claim 1, wherein the one or more protection policiesassociated with the working-protection arrangement include one or moreof the following: routing constraints, link cost, pre-emption, diversityrequirements, and service level guarantees.
 10. A system, comprising: acontrol plane configured to establish a current working pathcorresponding to a first path through a network between a first locationand a second location and a current protect path corresponding to asecond path through the network between the first location and thesecond location, the current working path and the current protect pathforming a current working-protection arrangement configured tofacilitate communication between the first and second locations; and aprotection policy server configured to receive information associatedwith the establishment of the current working path and current protectpath, the protection policy server further configured to: (1) receivenotification of a failure of the current working path and currentprotect path; (2) determine what type of new working path and newprotect path need to be created based at least in part on one or moreprotection policies associated with the working-protection arrangementbetween the first location and the second location; (3) establish viathe control plane the new working path and the new protect path throughthe network between the first location and the second location andrelease resources of at least one of the failed current working path andthe failed current protect path; (4) receive information associated withthe establishment of the new working path as the current working paththe new protect path as the current protect path; and (5) repeat Steps(1), (2), (3) and (4) each time a failure occurs on at least one of thecurrent working path and current protect path.
 11. The system of claim10, wherein the notification received in Step (1) indicates that therewas a failure on the current working path which facilitated areassignment of the current protect path to be the current working path.12. The system of claim 10, wherein the current protect path is adedicated protection path used to simultaneously carry the same trafficas the current working path when the current working path is in a normaloperating mode.
 13. The system of claim 10, wherein the current protectpath is a shared protection path that is used to carry preemptabletraffic when the current working path is in a normal operating mode. 14.The system of claim 10, wherein the current protect path operates as ashared protection path for two or more working paths which include thecurrent working path when all such working paths are in a normaloperating mode.
 15. The system of claim 10, wherein the informationassociated with the establishment of the current working path andcurrent protect path comprises information identifying all segmentsalong both the current working path and current protect path.
 16. Thesystem of claim 10, wherein said control plane is an intelligent controlplane in an optical transport network.
 17. The system of claim 10,wherein establishing the new working path and the new protect pathcomprises dynamically allocating bandwidth for the new working path andthe new protect path from a pool of available bandwidth resources in thenetwork, rather than from pre-reserved dedicated bandwidth.
 18. Thesystem of claim 10, wherein the one or more protection policiesassociated with the working-protection arrangement include one or moreof the following: routing constraints, link cost, pre-emption, diversityrequirements, and service level guarantees.
 19. A method, comprising:(1) in response to a request for service, establishing a current workingpath corresponding to a first path through an optical transport networkbetween a first location and a second location, and a current protectpath corresponding to a second path through the optical transportnetwork between the first location and the second location, the currentworking path and the current protect path forming a currentworking-protection arrangement configured to facilitate communicationbetween the first and second locations; (2) receiving notification ofall segments along both the current working path and current protectpath; (3) receiving notification of a protection switching event thatinvolves failure of the current working path and the current protectpath; (4) determining what type of new working path and new protect pathneed to be created based at least in part on one or more protectionpolicies associated with the working-protection arrangement between thefirst location and the second location; (5) establishing the new workingpath and the new protect path through the optical transport networkbetween the first location and the second location to take the place ofthe current working path and the current protect path and releasingresources of the failed current working path and the current protectpath; (6) receiving notification of the establishment of the new workingpath as the current working path and the new protect path as the currentprotect path; and (7) repeating Steps (3), (4), (5) and (6) onoccurrence of a failure on the current working path.